Disc-shaped recording medium, cutting apparatus for same, and disc drive

ABSTRACT

There is provided an optical disc having preformed thereon a spiral wobbled track as a grove and/or land along with data is to be recorded. The track is wobbled for a series of predetermined signal units each composed of an FSK information bit part based on a waveform resulted from FSK modulation of information bit and a singe-frequency part based on a waveform of a single frequency. The FSK modulation uses two different frequencies of which the one is the same as the single frequency and the other is different from the single frequency. These different frequencies are in such a relation that each of them has an even number of wobbles and an odd number of wobbles alternately in a predetermined cycle.

TECHNICAL FIELD

The present invention generally relates to a disc-shaped recordingmedium such as an optical disc, a cutting apparatus for use inproduction of the disc-shaped recording medium and a disc drive forrecording and/or reproducing data to and/or from the disc-shapedrecording medium, and more particularly to a disc-shaped recordingmedium having a wobbled track as a pregroove formed thereon.

BACKGROUND ART

To record data to an optical disc which is a disc-shaped recordingmedium, a guiding means is required for forming a recording track. Tothis end, pregrooves are preformed on the optical disc and the grooveitself or a land, of which the cross section is trapezoidal, between thepreformed grooves is used as the recording track.

Address information has to be recorded on an optical disc of this typeto permit recording of data in a given position on a recording track onthe optical disc. In some cases, such address information is recorded onthe optical disc by wobbling a groove. Namely, a data recording track ispreformed as a pregroove for example on the optical disc while thelateral wall of the pregroove is being wobbled correspondingly to theaddress information. Thus, for recording or reproducing data to or fromthe optical disc, an address to which the data is to be written or fromwhich the data is to be read can be read from wobbling informationprovided as return light information, and the data can be written to adesired position or read from a desired position without having topreform pit data or the like indicating an address, for example, on therecording track.

By additionally recording address information as a wobbled groove, itwill be unnecessary to discretely define an address area on a track andrecord an address as pit data in such address area, for example.Therefore, the actual capacity of the optical disc for recording datacan be increased for the address area which is thus made unnecessary.

Absolute time (address) information represented by such a wobbled grooveis called ATIP (absolute time in pregroove) or ADIP (address inpregroove).

Optical discs having such a wobbled groove formed thereon include CD-R(CD-Recordable), CD-RW (CD-Rewritable), DVD-R, CD-RW, DVD+RW, etc. Inthese types of optical discs, however, address information isadditionally recorded as a wobbled groove in a manner different from onetype to another of these optical discs.

In CD-R and CD-RW, the groove is wobbled according to a signal generatedby making FM modulation of address information.

ATIP information embedded in a wobbled groove formed on CD-R/CD-RW issubjected to biphase modulation before the FM modulation as shown inFIG. 1. More specifically, the biphase modulation is such that ATIP datasuch as an address or the like is changed in state between “1” and “0”in each predetermined cycle by the biphase modulation and its ratiobetween average numbers of “1” and “0” is 1:1, and a wobbling signal of22.05 kHz in average frequency are generated by the FM modulation of theATIP data.

A groove defining a recording track is wobbled according to such an FMmodulation signal.

In DVD-RW which is a phase-change recording-based rewritable version ofDVD (digital versatile disc) and DVD-R which is an organic dyechange-based recordable version of DVD, wobbled grooves G are formed aspreformatted on the disc and a land prepit LPP is formed in a landbetween the grooves G, as shown in FIG. 2.

In this case, the wobbled groove is used to control the rotation of thedisc and generate a recording master clock or for similar purposes, andthe land prepit is used to determine an accurate recording position inbits and acquire a variety of information about the disc such as apre-address etc. In this case, the pieces of address informationthemselves are recorded as land prepits LPP, not as wobbles of thegroove.

In DVD-RAM which is the phase change recordable version of DVD,information such as an address is recorded as a groove wobbled based onthe phase modulation (PSK modulation) on the disc.

FIGS. 3A to 3C show information represented by phase modulation-basedwobbles of the groove. As shown in FIGS. 3A to 3C, eight wobbles aretaken as one ADIP unit. Each of the wobbles is phase-modulated for apositive wobble PW and negative wobble NW to take place alternately in apredetermined order, so that the ADIP unit represents a sync pattern ordata “0” or “1”.

Note that the positive wobble PW is a wobble whose leading end isdirected toward the inner circumference of the disc, and the negativewobble NW is a wobble whose leading end is directed toward theouter-circumference of the disc.

FIG. 3A shows a sync pattern (ADIP sync unit). In this sync pattern, theformer four wobbles (W0 to W3) are negative ones NW and the latter fourwobbles (W4 to W7) are positive ones PW.

FIG. 3B shows an ADIP data unit being the data “0”. In this ADIP dataunit, the leading wobble W0 is a negative one NW as a bit sync, it isfollowed by three wobbles W1 to W3 as positive ones PW, and the latterfour wobbles include two wobbles W4 and W5 as positive wobbles PW andtwo wobbles W6 and W7 as negative ones NW. Thus, the ADIP data unitrepresents data “0”.

FIG. 3C shows an ADIP data unit being the data “1”. In this ADIP dataunit, the leading wobble W0 is a negative one NW as a bit sync, it isfollowed by three wobble W1 to W3 as positive ones PW, and the latterfour wobbles include two wobbles W6 and W7 as negative ones NW and twowobbles W6 and W7 as positive ones PW. Thus, the ADIP data unitrepresents data “1”.

These ADIP units represent together one channel bit, and a predeterminednumber of such ADIP units represents an address or the like.

However, the above wobbling techniques are not advantageous as follows:

First, in case a groove is wobbled according to FM modulation data as inCD-R and CD-RW, the stroke of a wobble of an adjacent track will cause aphase change of the FM waveform. Thus, in case the track pitch isreduced, an address as ATIP data cannot be reproduced well. In otherwords, the FM modulation data-based wobbling cannot suitably be used incase the track pitch is narrowed for an improved recording density.

Next, in case land prepits are formed as in DVD-R and DVD-RW, the landprepits may possibly have a cross talk into a read RF signal, causing adata error and mastering (cutting) has to be done for the groove andland prepits (2-beam mastering). This is relatively difficult toimplement.

Further, in case a groove is wobbled according to PSK data as in DVD-RW,the RF component at the phase-change point of a PSK modulation wave maypossibly have a crosstalk into a read RF signal, causing a criticalerror.

Also, since the PSK phase shift point has an extremely high frequencycomponent, the essential frequency band of a wobbling signal processingcircuit system will be higher.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention has an object to overcome theabove-mentioned drawbacks of the related art by providing a novel andimproved disc-shaped recording medium in which a groove is wobbled by awobbling method suitable for an increased recording capacity andimproved write-read characteristics of the recording medium, a cuttingapparatus for production of the disc-shaped recording medium, and a discdrive compatible with the disc-shaped recording medium.

The above object can be attained by providing a disc-shaped recordingmedium having preformed thereon a spiral, wobbled track as a groove orland along which data is recorded, wherein the wobble of the track is aseries of predetermined signal units each consisting of an FSKinformation bit part corresponding to a waveform resulted from FSK(frequency shift keying) modulation of information bit and asingle-frequency part corresponding to the waveform of a singlefrequency.

For the above disc-shaped recording medium, two different frequenciesare used in the FSK modulation. One of the frequencies is the same asthe single frequency while the other frequency is different from thesingle frequency. These frequencies are in such a relation that each ofthem has an even number of waves and an odd number of waves alternatelyin a predetermined cycle. For example, the other frequency has afrequency 1.5 times or 1/1.5 times higher than that of the onefrequency.

In the FSK information bit part, a 2-wave period of a frequency as thesingle frequency corresponds to one channel bit as information bit.

The period length of the FSK information bit part is an integralmultiple of the period of the single frequency. In the predeterminedunit, the period length of the single-frequency part is more than about10 times of that of the FSK information bit part.

According to the present invention, the integral multiple of thepredetermined units corresponds to a time length in a recording unit ofdata to be recorded to the track.

The channel clock frequency of the data to be recorded to the track isan integral multiple of the single frequency. The frequency as thesingle frequency is a one between a tracking servo frequency band andread signal frequency band.

The FSK information bit part is formed on the basis of a waveformresulted from FSK modulation of information bit as address information.The FSK modulation for the FSK information bit part uses two differentfrequencies. One of these frequencies is continuous in phase with theother at the point of shift from one to the other.

According to the present invention, the FSK modulation is an MSK(minimum shift keying) modulation. In the FSK information bit partresulted from MSK modulation of the information bit, a 4-wave period ofthe frequency as the single frequency corresponds to one channel bit asinformation bit. In this case, the FSK information bit part resultedfrom MSK modulation of the information bit includes two differentfrequencies of which the one is the same as the single frequency and theother is a frequency x times higher than the single frequency. The4-wave period includes a period of four waves of the one frequency and aperiod of x waves of the other frequency and three waves of the onefrequency. For example, x=1.5.

Also, the above object can be attained by providing a cutting apparatusincluding according to the present invention:

means for generating a series of predetermined signal units eachcomposed of a signal part resulted from FSK modulation of informationbit and a signal part of a single frequency;

means for generating a drive signal on the basis of the signal suppliedfrom the signal generating means;

a laser source means;

means for deflecting laser light from the laser source means on thebasis of the drive signal from the drive signal generating means; and

means for cutting a disc substrate by radiating the laser light to thedisc substrate through the laser light deflecting means to form, on thedisc substrate, a wobbled track including a series of predeterminedunits each composed of an FSK information bit part based on a waveformresulted from FSK modulation of the information bit and asingle-frequency part based on the waveform of the single frequency.

Also, the above object can be attained by providing a disc drive forrecording or reproducing data to or from the aforementioned disc-shapedrecording medium according to the present invention, the apparatusincluding according to the present invention:

a head means for radiating laser light to a track to generate a returnlight signal;

means for extracting a wobbling signal about wobbling of the track fromthe return light signal; and

a wobbling information decoding means for making FSK demodulation of thewobbling signal to decode information represented by the informationbit.

More specifically, the wobbling information decoding means includes aclock reproduction unit to generate, by a PLL, a wobble reproductionclock on the basis of a signal corresponding to a single-frequency partof the wobbling signal, an FSK demodulator to make FSK demodulation ofthe wobbling signal corresponding to an FSK information bit part of thewobbling signal to provide demodulation data, and a decoder to decoderequired information composed of the information bit from thedemodulation data supplied from the FSK demodulator.

The FSK demodulator includes a correlation detection circuit to make FSKdemodulation by detecting a correlation between the wobbling signal anda delay signal resulted from delaying of the wobbling signal by a periodof the wobble reproduction clock.

The FSK demodulator includes also a frequency detection circuit to makeFSK demodulation by detecting a number of rising edges or falling edgesof the wobbling signal, existent within one period of the wobblereproduction clock.

In case the FSK demodulator includes the above correlation detectioncircuit and frequency detection circuit, the decoder decodes therequired information using both the demodulation data demodulated by thecorrelation detection circuit and that demodulated by the frequencydetection circuit. Particularly, the decoder decodes the requiredinformation from a logical product of the demodulated data from thecorrelation detection circuit and that from the frequency detectioncircuit when the PLL is being pulled in the clock reproduction unit, andit decodes the required information from a logical sum of thedemodulated data from the correlation detection circuit and that fromthe frequency detection circuit when the PLL is stable in the clockreproduction unit.

The decoder includes a gate generator to generate a gate signal for thePLL in the clock reproduction unit based on the fact that it decodessync information as one of the required information, and the PLLfunctions on the basis of the gate signal to provide a PLL operationbased solely on a part, corresponding to the single frequency, of thewobbling signal.

The disc drive according to the present invention further includes aspindle servo means for making spindle servo control using the wobblereproduction clock, and means for generating an encode clock synchronouswith the wobble reproduction clock and which is to be used for encodingdata to be recorded.

The wobbling information decoder also includes an MSK demodulator formaking MSK modulation of an MSK modulation signal corresponding to theFSK information bit part of the wobbling signal to generate demodulationdata. The MSK demodulator demodulates the MSK modulation signal in unitsof the 4-wave period of the frequency as the single frequency to providethe modulation signal.

The wobbling method adopted in the present invention is Such that awobbled track is formed as a series of predetermined units eachincluding an FSK information bit part and a single-frequency part basedon the waveform of a single frequency. That is, since the FSK (MSK) ispartial, the wobbling is little influenced by any crosstalk. Also, sincethe land such as the land prepits has no missing part, there will nottake place any influence of any land missing-part on data to berecorded. Since no pits are formed in the land, mastering can be madewith a single beam. Further, the wobbling has no high frequencycomponent as in the PSK.

These objects and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription of the best mode for carrying out the present invention whentaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 explains an FM modulation-based wobbling.

FIG. 2 explains forming of land prepits.

FIGS. 3A, 3B and 3C show information represented by phase-modulatedwobbles of a groove.

FIG. 4A is a plan view of a first embodiment of the optical discaccording to the present invention, having a wobbled groove formedthereon, and FIG. 4B is a partial perspective view of the optical disc.

FIG. 5 explains a wobble unit on the optical disc according to thepresent invention.

FIG. 6 explains an FSK information bit part of wobbling of the groove onthe optical disc according to the present invention.

FIG. 7 explains an ECC block on the optical disc according to thepresent invention.

FIG. 8 explains a RUB structure.

FIGS. 9A and 9B explain an address structure on the optical discaccording to the present invention.

FIGS. 10A and 10B explain an address structure on the optical discaccording to the present invention.

FIG. 11 is a block diagram of the cutting apparatus used for productionof the optical disc according to the present invention.

FIG. 12 is a block diagram of the disc drive according to the presentinvention.

FIG. 13 is a block diagram of the wobbling circuit included in the discdrive according to the present invention.

FIG. 14 is a block diagram of the correlation detection circuit includedin the disc drive according to the present invention.

FIGS. 15A to 15G show waveforms indicating points of time at which thecorrelation detection circuit is actuated.

FIG. 16 is a block diagram of the frequency detection circuit includedin the disc drive according to the present invention.

FIGS. 17A to 17E show waveforms indicating points of time at which thefrequency detection circuit is actuated.

FIGS. 18A to 18F explain an MSK stream of wobbles on a second embodimentof the optical disc according to the present invention.

FIGS. 19A to 19C explain a bit structure by wobbles on the secondembodiment of the optical disc according to the present invention.

FIGS. 20A and 20B explain an address block for the RUB on the secondembodiment of the optical disc according to the present invention.

FIGS. 21A to 21C explain a sync signal part on the second embodiment ofthe optical disc according to the present invention.

FIGS. 22A to 22E explain a sync bit pattern on the second embodiment ofthe optical disc according to the present invention.

FIGS. 23A and 23B explain a data part on the second embodiment of theoptical disc according to the present invention.

FIGS. 24A to 24C explains an ADIP bit pattern on the second embodimentof the optical disc according to the present invention.

FIG. 25 is a block diagram of the MSK demodulator used for the secondembodiment of the optical disc according to the present invention.

FIGS. 26A and 26B explain the MSK demodulation with the aid of waveformsobserved when the length (L) of the wobble detection window is L=4.

FIGS. 27A and 27B explain the MSK demodulation with the aid of waveformsobserved when the length (L) of the wobble detection window is L=2.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described herebelow concerning itsapplications to an optical disc, a cutting apparatus for use inproducing the optical disc, and a disc drive for recording andreproducing data to and from the optical disc.

The description of the present invention will be given in the followingorder:

First Embodiment

1-1 Physical characteristics of the optical disc

1-2 Wobbling method

1-3 Cutting apparatus

1-4 Disc drive

Second Embodiment

2-1 Wobbling method

2-2 Demodulation

First Embodiment

1-1 Physical Characteristics of the Optical Disc

The physical characteristics of the optical disc according to thepresent invention and a wobbled track formed on the optical disc will bedescribed below:

The optical disc according to the present invention is included in thecategory of discs called “DVR (data and video recording)” for example.It adopts a novel wobbling method dedicated for DVR.

Table 1 shows the typical parameters of the first embodiment of theoptical disc according to the present invention. TABLE 1 Laserwavelength 405 nm Numerical aperture (NA) 0.85 Disc diameter 120 mm Discthickness 1.2 mm Diametrical position of information area 44 to 117 mmTrack pitch 0.30 μm Channel bit length 0.086 μm Data bit length 0.13 μmCapacity for user data 22.46 Gbytes Average rate of user data transfer35 Mbits/sec Recording method Phase-change/ in-groove recording

The first embodiment of the optical disc according to the presentinvention is a one using the phase-change recording method for recordingdata thereto. The disc has a diameter of 120 mm and a thickness of 1.2mm. These diameter and thickness of the optical disc according to thepresent invention are similar to those of CD (compact disc) and DVD(digital versatile disc).

Like the conventional similar types of discs, the first embodiment ofthe optical disc has defined thereon a lead-in area, program area and alead-out area, counted from the inner circumference thereof. Theinformation area including these areas diametrically covers an arearanging from 44 mm to 117 mm.

The wavelength of the laser light used for recording or reproducing datais 405 nm. According to the present invention, the laser light is aso-called blue laser. To focus the laser light radiated to the opticaldisc on the signal recording layer of the optical disc, there is used anobjective lens having a numerical aperture (NA) of 0.85.

The track pitch of the recording track is 0.30 μm, channel bit length is0.086 μm, and the data bit length is 0.13 μm. The optical disc has acapacity of 22.46 Gbytes for recording user data. User data can betransferred at an average rate of 35 Mbits per second.

Data is recorded by the groove recording method. Namely, a groove isalready formed as a recording track on the optical disc, and data isrecorded in the groove.

FIG. 4A illustrates, in the form of a plan view, a first embodiment ofthe optical disc according to the present invention. The optical disc isindicated with a reference 100. In this optical disc 100, embossed pitsEP are preformatted at the innermost circumference side and a groove GVis formed in a range from next to the embossed pits EP to the outercircumference side, as shown. The groove GV is formed spirally from theinner circumference toward the outer circumference of the optical disc.It should be noted that the groove GV may be formed concentrically asanother embodiment. Wobbles of such a groove GV represent physicaladdresses.

FIG. 4B is a schematic partial perspective view of an optical disc. Theoptical disc is indicated with a reference 1. As shown, the optical disc1 has a groove GV formed thereon. The lateral wall of the groove GV arewobbled adaptively to address information or the like, that is,correspondingly to a signal generated based on an address or the like. Aland L lies between two adjacent grooves GV. Data is recorded in thegroove GV as mentioned above. That is, the groove GV serves as arecording track. It should be noted that alternatively, data may berecorded on the land L, as a recording track or in the groove GV and onthe land L.

The present invention provides an optical disc featured by a wobbling ofthe groove, which will be described in detail later. Briefly, with thegroove wobbled adaptively to a signal generated by FSK modulation of anaddress or the like, the optical disc according to the present inventionis suitably usable as a high-density, large-capacity disc.

Note that data is written or read to or from the optical disc 100 beingrotated at a CLV (constant linear velocity). The CLV rotation is alsoapplied when data is recorded in the groove GV. Therefore, the number ofwobbles of a groove for one turn of track will be larger as the groovegoes toward the outer circumference of the optical disc.

1-2 Wobbling Method

Next, how to wobble the groove will be described:

FIG. 5 shows the structure of a wobble unit on the optical discaccording to the present invention. The groove is wobbled to define aseries of the wobble units shown in FIG. 5. As shown, each wobble unitis composed of an FSK information bit part and a single-frequency part.The single-frequency part includes only wobbles of a wobbling frequencyfw1. For this part, the groove is wobbled in a fixed cycle correspondingto the frequency fw1. This single-frequency part provides a series of 65wobbles of the frequency fw1 for example. It should be noted that thesingle-frequency wobble of the frequency fw1 is also called “monotonewobble”. On the other hand, the FSK information bit part includeswobbles resulted from FSK modulation of ADIP information, made using twodifferent frequencies, of which the one is the same as the frequency fw1of the monotone wobble and the other is a frequency fw2 other than themonotone-wobble frequency. The time length of the FSK information bitpart corresponds to a length of six monotone wobbles.

It is just an example that the single-frequency part has a period of 65monotone wobbles while the FSK information bit part has a period of sixmonotone wobbles as above, and it should be noted that thesingle-frequency part may have a period of 60 monotone wobbles, forexample. However, it is effective for a reduction of the adverse effectof crosstalk as well as for easier and quicker PLL locking for thereduction that the single-frequency part is sufficiently longer than theFSK information bit part. For example, the single-frequency part shouldpreferably be more than about 10 times longer in period than the FSKinformation bit part. Therefore, in case the FSK information bit part isset to have a period of six monotone wobbles, the single-frequency partshould be set to have a period of more than 60 monotone wobbles. Thisdoes not means that the single-frequency part should never be set tohave a period of less than 59 monotone wobbles. Practically, however,the period of the single-frequency part should properly be set withconsiderations given to requirements such as permissible ranges of thecrosstalk, PLL locking time, etc.

One FSK information bit part having a period of six monotone wobblesrepresents one information bit as ADIP data. As shown in FIG. 5, anaddress or the like as ADIP data is represented by information bits fromADIP units 0 to N as the FSK information bit parts discretely positionedalternately with single-frequency parts.

Because of the address structure of the ADIP data which will bedescribed in detail later, the frequency fw1 of the monotone wobble is478 or 957 kHz, for example. On the other hand, the other frequency fw2used for the FSK modulation is 1.5 times higher than the frequency fw1,for example. That is, the frequency fw2 is 717 or 1435.5 kHz. However,the values of the frequencies fw1 and fw2 are not limited to theabove-mentioned ones. For example, the frequency fw2 may be 1/1.5 timeshigher than the frequency fw1. In addition, the frequencies fw1 and fw2should preferably be in such a relation that even and odd numbers ofwobbles are made with both the frequencies in a predetermined cycle. Incase the frequency fw2 is 1.5 times higher than the frequency fw1 asabove, the period of six wobbles of the frequency fw1 will correspond tothat of nine wobbles of the frequency fw2, which meets the aboverelation for the even and odd numbers of wobbles made in thepredetermined cycle. If this requirement is met, the FSK demodulationcan be made more easily in the disc drive which will be described indetail later.

The information bit represented by the FSK information bit part composedof the wobbles resulted from the FSK modulation of the ADIP information,effected using the two different frequencies fw1 and fw2, will bedescribed below with reference to FIG. 6. It should be noted that in thefollowing description, the frequencies fw1 and fw2 are in a relation of1:1.5.

In the FSK information bit part having the period of six monotonewobbles, a period of two monotone wobbles is taken as one channel bit.Therefore, in one FSK information bit part (one ADIP unit), threechannel bits form together one information bit. The FSK modulation ismade so that the frequency fw1 is a channel bit “0” while the frequencyfw2 is a channel bit “1”. That is, in the period of two monotone wobblesof the frequency fw1, two wobbles of the frequency fw1 is “0” whilethree wobbles of the frequency fw2 is “1”. Such three channel bits inone FSK information bit part represent information bits such as clustersync, secondary sync, data “0” and data “1”. Three channel bits being“1”, “1” and “1”, respectively, represent a cluster sync. In this case,nine wobbles of the frequency fw2 are included in series in a period ofsix monotone wobbles, as shown in FIG. 6. Three channel bits being “1”,“1” and “0”, respectively, represent a secondary sync. In this case, sixmonotone wobbles of the frequency fw2 are included in series in a periodof four monotone wobbles, and a period of two monotone wobbles,following the period of four monotone wobbles, includes two wobbles ofthe frequency fw1. Three channel bits being “1”. “0” and “0”,respectively, represent data “0”. In this case, a series of threewobbles of the frequency fw2 is included in a period of two monotonewobbles, and a period of four monotone wobbles, following the 2-wobbleperiod, includes four wobbles of the frequency fw1. Three channel bitsbeing “1”, “0” and “1”, respectively, represent data “1”. In this case,three wobbles of the frequency fw2 are included in series in a firstperiod of two monotone wobbles, a period of two monotone wobbles,following the first period, includes two wobbles of the frequency fw1,and a series of three wobbles of the frequency fw2 is included in thelast period of two monotone wobbles.

As above, one FSK information bit part, that is, one ADIP unit as shownin FIG. 5, represents one information bit, and such ADIP informationbits are gathered to form address information. Address informationrepresenting one address on the disc is of 98 bits, for example. In thiscase, 98 ADIP units partially laid as a wobbled groove are gathered toform address information. This will further be described later withreference to FIGS. 9 and 10.

In this embodiment, an integral multiple of wobble units each being apredetermined unit of wobbling corresponds to the time length of a datarecording unit to be recorded along a track. The data recording unit iscalled RUB (recording unit block). One RUB includes an integer number ofaddresses. In the following, there will be described examples of oneaddress in one RUB and two addresses in one RUB, respectively.

As above, the address is information included in the 98 ADIP units. Incase one address is included one RUB, a section of 98 wobble unitscorresponds to a section where data is recorded as one RUB. In case twoaddresses are included in one RUB, a section of 196 wobble unitscorresponds to a section where data is recorded as one RUB.

First, the structure of an ECC (error correction code) block of data tobe recorded will be described with reference to FIG. 7 for explanationof RUB as a unit of the to-be-recorded data.

One ECC block is also called “cluster”. It is one block formed by addingan error correction code to data to be recorded. As shown in FIG. 7, theECC block is composed of 495 rows of recording frame of 1932T (where Tis a channel clock period of the data). One ECC block is of 64 kbytes.For example, the ECC block consists of data and parity as shown in FIG.7.

The “1932T” corresponds to 28 monotone wobbles of the frequency fw1(=957 kHz) or 14 monotone wobbles of the frequency fw1 (=478 kHz). Morespecifically, 69 channel clock periods T of data (with the frequency fw1of 957 kHz), or 138 channel clock periods T of data (with the frequencyfw1 of 478 kHz), correspond to one monotone wobble period of thefrequency fw1. The channel clock frequency of the data is 66.033 kHzwhich corresponds to 957 kHz×69 or 478 kHz×138. That is, the channelclock frequency of the data is an integral multiple of the monotonewobble frequency, which means that an encoded clock for data recordingcan easily be generated from a wobble clock reproduced by the PLL from amonotone wobble of a wobbled groove.

Addition of a run-in and run-out to the ECC block shown in FIG. 7 yieldsa RUB (recording unit block) as shown in FIG. 8. RUB is composed of aguard GD and preamble PrA as a run-in of 1932T at the beginning of theECC block, and a postamble PoA and guard GD as a run-out of 1932T at theend of the ECC block, as shown in FIG. 8. Therefore, the RUB is a blockof 1932T×497 rows, which is a unit for data recording. One or two piecesof address information as ADIP information correspond to such a RUB.First, an example of one address corresponding to one RUB will bedescribed with reference to FIGS. 9A and 9B and Table 2. In case oneaddress corresponds to one RUB, the frequency fw1 of the monotone wobbleis 478 kHz. The period of one wobble corresponds to 138T. In this case,since one recording frame of 1932T of RUB corresponds to a period of 14wobbles, one RUB will correspond to a period of 14×497 (=6958) monotonewobbles as shown in FIG. 9A. In case one address corresponds to oneaddress, the periods of 6958 monotone wobbles is taken as one address(ADIP) block.

Since an address is formed from a block of 98 bits as above, 98 wobbleunits will be laid in a period of 6958 monotone wobbles as shown in FIG.9B. One wobble unit will have a length corresponding to a period of 71monotone wobbles. That is, one wobble unit is composed of an FSKinformation bit part whose period is of six monotone wobbles included inan ADIP unit, and 65 monotone wobbles.

One information bit as shown in FIG. 6 is taken from each of 98 ADIPunits to form address information of 98 bits. The bits included in theaddress information are as shown in Table 2: TABLE 2 Total 98 bitsDescription Primary sync 1 bit Cluster sync Auxiliary bits 9 bitsCluster address 24 bits (3 bytes) Auxiliary data 40 bits (5 bytes) ECC24 bits (3 bytes)

The top one bit is sync information. It corresponds to a cluster sync.The next 9 bits are auxiliary information bits. The further 24 bits (3bytes) define a value of cluster address. The next 40 bits (5 bytes) areauxiliary information bits. The last 24 bits (3 bytes) form an ECC forthe address information.

In case two addresses are included in one RUB, the address informationof 98 bits is composed as shown in FIG. 10 and Table 3. TABLE 3 Total 98bits Description Primary sync 1 bit ½ cluster sync Auxiliary bits 9 bits½ cluster address 24 bits (3 bytes) 2 addresses per cluster Auxiliarydata 40 bits (5 bytes) ECC 24 bits (3 bytes)

In the above case, the frequency fw1 of the monotone wobble is 957 kHz.The period of one wobble corresponds to 69T. In this case, since onerecording frame 1932T of RUB corresponds to a period of 28 wobbles, oneRUB will correspond to a period of 13916 (=28×497) monotone wobbles asshown in FIG. 10A. In case two addresses are included in one RUB, aperiod of 6958 monotone wobbles, being a half period of one RUB, is oneaddress (ADIP) block. Since an address is formed from a 98-bit block inthis case as well, 98 wobble units will be included in a period of 6958monotone wobbles, being a half period of one RUB. One wobble unitcorresponds to the length of a period of 71 monotone wobbles, as shownin FIG. 10B.

Therefore, an FSK information bit part having a period of six monotonewobbles, being an ADIP unit, and 65 monotone wobbles form together onewobble unit as shown in FIGS. 9A and 9B.

One information bit is taken from each of 98 ADIP units to form addressinformation of 98 bits. The bits included in the address information areas shown in FIG. 10. The top one bit is sync information. It correspondsto a cluster sync for a half cluster. The next 9 bits are auxiliaryinformation bits. The further 24 bits (3 bytes) define an address valueof the half cluster. The next 40 bits (5 bytes) are auxiliaryinformation bits. The last 24 bits (3 bytes) form an ECC for the addressinformation.

The wobbling method adopted in the present invention has been describedin the above. In effect, the wobbling method in the present invention isfeatured as follows:

For wobbling of a track, a predetermined wobble unit is formed from anFSK information bit part corresponding to a waveform resulted from FSKmodulation of information bit and a single-frequency part correspondingto the waveform of a single frequency fw1 and such wobble units arecontinuously connected in series. That is, the FSK information bit parthaving actual information bit embedded therein will partially exist on awobbled track (groove). The partial existence of the FSK information bitpart permits to considerably reduce the adverse effect of crosstalk evenwhen the track pitch is narrow.

Two different frequencies fw1 and fw2 are used in the FSK modulation toform the FSK information bit part. The frequency fw1 is the same as thefrequency of the monotone wobble, and the frequency fw2 is 1.5 timeshigher than the frequency fw1 for example as mentioned above. Thus,these frequencies fw1 and fw2 are in such a relation that each of themhas an even number of wobbles and an odd number of wobbles alternatelyin a predetermined cycle.

In the FSK information bit part, a 2-wobble period of the monotonewobble is one channel bit as information bit. The period of the FSKinformation bit part corresponds to the period of six wobbles, namely,to a period corresponding to an integral multiple of the monotone wobbleperiod. These features contribute to an easier FSK modulation.

In the wobble unit, the period length of the single-frequency part ismore than about 10 times longer than that of the FSK information bitpart. Thus, the sufficiently long period of the single-frequency part inrelation to that of the FSK information bit part can facilitate thereduction of adverse effect of crosstalk.

In a relation between the wobbling and recorded data, the integralmultiple of the predetermined units corresponds to a time length of RUBbeing a recording unit of data to be recorded on the track. An integralnumber of addresses, one or two, as ADIP information will be included inone RUB. These features lead to matching between the wobbled groove anddata to be recorded in the groove.

The channel clock frequency of the data to be recorded to the track isan integral multiple of the single frequency fw1 of the monotone groove.Thus, an encode clock for the data recording can easily be generated bydividing the wobble clock generated based on the wobbling.

The frequency fw1 of the monotone wobble is 478 or 957 kHz for exampleas above. This frequency is of a frequency band between the trackingservo frequency band (near 10 kHz) and read signal frequency band(several or more MHz). This feature makes it possible to separate andextract ADIP information represented by wobbles without any interferencebetween the servo signal and read signal.

The aforementioned FSK modulation is an MSK (minimum shift keying) asone of the FSK modulation techniques. In the FSK modulation, amodulation index H is defined and two frequencies f1 and f2 are used.The modulation index is H=|f1−f2|/fb where fb is a transmission rate ofa signal to be modulated. The modulation index is normally 0.5≦H≦1.0. AnFSK whose modulation index H is 0.5 is called ““MSK”.

According to the present invention, the two different frequencies fw1and fw2 are continuous in phase with each other at the point of shiftfrom one to the other in the FSK information bit part. Thus, the FSKinformation bit part will not have any high frequency component as inthe wobbling by the PSK.

1-3 Cutting Apparatus

Next, the cutting apparatus used for producing the disc having a wobbledtrack formed thereon will be described.

The disc producing process generally consists of a so-called masteringprocess and a replicating process. The mastering process covers thesteps of production down to completion of a stamper for use in thereplication process, and the replication process coves the steps ofproductions in which the stamper is used for mass production of opticaldiscs as the replica of the stamper.

More specifically, in the mastering process, a polished glass substrateis applied with photo resist, the photo resist layer is exposed to alaser beam to form pits and grooves in the photo resist layer (this isthe so-called “cutting”).

In this embodiment, pits are cut in a portion of the photo resist layer,corresponding to the embossed area at the innermost circumference sideof the disc, and a wobbled groove is cut in a portion corresponding tothe groove area.

Dare for the pits in the embossed area is prepared in a process called“premastering”.

After completion of the cutting, the photo resist layer is subjected topredetermined processes such as development, and information istranscribed to the metallic surface by electroforming for example toform a stamper necessary to replicate the disc.

Next, the stamper is used to transcribe information to the resinsubstrate by the injection process for example to form a reflectinglayer on the resin substrate, and then a final product is finished bymaking processes such as shaping of the substrate into a desired disc.

Referring now to FIG. 11, the cutting apparatus according to the presentinvention is illustrated in the form of a block diagram. As shown, thecutting apparatus includes an optical system 70 in which a laser beam isradiated to a glass substrate 71 having a photo resist layer formedthereon to cut the photo resist layer, a drive system 80 to rotate theglass substrate 71, and a signal processor 60 to convert input data intodata to be recorded and control the optical system 70 and drive system80.

The optical system 70 includes a laser source 72 which is an He-Cd laserfor example, an acousto-optical type optical modulator 73 (AOM) tomodulate (on/off) the laser beam coming from the laser source 72 basedon the data to be recorded, an acousto-optical type optical deflector(AOD) 74 to deflect the laser beam coming from the laser source 72 basedon a wobbling signal, a prism 75 to bend the optical axis of a modulatedlaser beam from the optical deflector 74, and an objective lens 76 toconverge the modulated laser beam reflected at the prism 75 and radiatethe converged laser beam to the photo resist surface on the glasssubstrate 71.

The drive system 80 includes a motor 81 to rotate the glass substrate71, an FG 82 to generate an FG pulse for detection of the rotation speedof the motor 81, a sliding motor 83 to slide the glass substrate 71radially thereof, and a servo controller 84 to control the rotationspeed of the motor 81 and sliding motor 83, tracking of th objectivelens 76, etc.

The signal processor 60 includes a formatting circuit 61 to form inputdata by adding an error correction code or the like to source data froma computer for example, and a logical operation circuit 62 to form datato be recorded by making a predetermined processing of the input datafrom the formatting circuit 61. The signal processor 60 also includes adata generator 63, parallel/serial converter 64 and a sign converter 66to generate a wobbling signal for wobbling a groove. The signalprocessor 60 further a synthesis circuit 65 to select one of the signalfrom the logical operation circuit 62 and that from the sign converter66 and output it as one continuous signal, and a drive circuit 68 todrive the optical modulator 73 and optical deflector 74 on the basis ofthe signal from the synthesis circuit 65. Further, the signal processor60 includes a clock generator 91 to supply a master clock MCK to thelogical operation circuit 62 etc., and a system controller 67 to controlthe servo controller 84, data generator 63, etc. on the basis of themaster clock MCK supplied from the clock generator 91. The master clockMCK supplied from the clock generator 91 is divided by N in a frequencydivider 92 to provide a bit clock “bit Ck”. The bit clock “bit Ck” isdivided by eight in a frequency divider 93 to provide a byte clock “byteCk”. The byte clock “byte CK” is supplied to a circuit system where itis required.

When cutting the photo resist layer on the glass substrate 71, the servocontroller 84 in the cutting apparatus according to the presentinvention controls the motor 81 to rotate the glass substrate 71 at aconstant linear velocity and the sliding motor 83 to slide the rotatingglass substrate 71 for a spiral track to be formed with a predeterminedtrack pitch.

At the same time, the outgoing laser beam from the laser source 72 ispassed to the optical modulator 73 and optical deflector 74 where itwill be modulated based on the data to be recorded, and the laser beamthus modulated is radiated from the objective lens 76 to the photoresist surface on the glass substrate 71. Thus, the photo resist isexposed based on the data and groove.

For cutting the embossed area at the innermost circumference side of thedisc, the input data having the error correction code or the like addedthereto by the formatting circuit 61, namely, the data to be recorded tothe embossed area, such as control data, is supplied to the logicaloperation circuit 62 where it is formed as data to be recorded.

At the timing of cutting the embossed area, the data to be recorded issupplied to the drive circuit 68 via the synthesis circuit 65. The drivecircuit 68 controls the optical modulator 73 to on-state at a time whenbits are to be formed, and to off-state at a time when no bits are to beformed, according to the data to be recorded.

With the above operations, an exposed portion corresponding to anembossed pit is formed on the glass substrate 71.

At a time of cutting the groove area, the system controller 67 controlsthe sequential outputting of data supplied from the data generator 63and corresponding to the FSK information bit part and singe-frequencypart. For example, the data generator 63 generates a series of data “O”on the basis of the byte clock “byte Ck” for a period corresponding tothe single frequency. Also, for a period corresponding to the FSKinformation bit part, the data generator 63 generates necessary datacorrespondingly to each of ADIP units forming together theaforementioned address block. That is to say, the data generator 63generates channel bit data corresponding to a cluster sync, secondarysync, data “0” and data “1” at a time corresponding to each FSK period.Of course, the data generator 63 generates the above data “0” or “1” insuch a predetermined order that data collected from the ADIP units willform a cluster address value and additional information. The data outputfrom the data generator 63 is formed into a serial data streamcorresponding to the bit clock “bit Ck” in the parallel/serial converter64, and supplied to the sign converter 66. The sign converter 66 usesthe so-called table lookup process to select a sine wave of apredetermined frequency correspondingly to the data supplied, andoutputs it. Therefore, for a period corresponding to the singlefrequency, the sign converter 66 will continuously output sine waves ofthe frequency fw1. Also, for a period corresponding to the FSKinformation bit part, the sign converter 66 will output either awaveform of the frequency fw2 or a one of the frequencies fw1 and fw2 asshown in FIG. 6 correspondingly to the content represented by the FSKinformation bit part, namely, any one of the cluster sync, secondarysync, data “0” and data “1”.

The synthesis circuit 65 supplies the drive circuit 68 with a signaloutput from the sign converter 66, that is, a signal of the singlefrequency or an FSK-modulated signal of the frequencies fw1 and fw2, asa wobbling signal. The drive circuit 68 will control the opticalmodulator 73 to on-state in order to form a groove. Also, the drivecircuit 68 will drive the optical deflector 74 correspondingly to thewobbling signal. Thus, the laser beam is wobbled, namely, a portionexposed as a groove is wobbled. With the aforementioned operations, anexposed portion corresponding to a wobbled groove is formed on the glasssubstrate 71 according to a format. Thereafter, the glass substrate 71is subjected to development, electroforming, etc. to produce a stamper,and the stamper is used to produce the aforementioned discs.

1-4 Disc Drive

Next, there will be described the disc drive according to the presentinvention to record data to the aforementioned optical disc andreproduce data recorded in the optical disc.

Referring now to FIG. 12, the disc drive according to the presentinvention is schematically illustrated in the form of a block diagram.The disc drive is generally indicated with a reference 30. An opticaldisc 100, constructed as explained above, is used as a recording mediumwith the disc drive 30.

For recording or reproducing data to or from the optical disc 100, theoptical disc 100 is set on a turntable 7 and rotated by a spindle motor6 at a constant linear velocity (CLV). A signal recording area on theoptical disc 100 being rotated is scanned by a laser light emitted froman optical pickup I to read pit data written to a track formed on theoptical disc 100 and ADIP information embedded as wobbles of the track.The pits recorded as data on the track formed as a wobbled groove areso-called phase-change pits, and pits formed in the innercircumference-side embossed area are so-called embossed pits.

The optical pickup 1 has disposed therein a laser diode 4 as a lasersource, a photodetector 5 to detect a return light from the optical disc100, an objective lens 2 to converge and focus the laser light on theoptical disc 100, and an optical system (not shown) to radiate the laserlight to the recording layer of the optical disc 100 through theobjective lens 2 and guide a return component of the laser light fromthe recording layer to the photodetector 5. Further the optical pickup Iincorporates a monitoring detector 22 to detect a part of output lightfrom the laser diode 4. The laser diode 4 emits a so-called blue laserof 405 nm in wavelength. The numerical aperture (NA) of the optical discis 0.85.

The objective lens 2 is supported by a biaxial mechanism 3 movably inboth tracking and focusing directions.

The optical pickup I is entirely movable by a sled mechanism 8 radiallyof the optical disc 100.

The laser diode 4 provided in the optical pickup I is driven by a drivesignal from a laser driver 18 to emit the laser light.

Information carried by the return light from the optical disc 100 isdetected by the photodetector 5 where it is converted into an electricalsignal corresponding to the light intensity of the detected light andsupplied to a matrix circuit 9 including a current-voltage conversioncircuit, matrix calculation/amplification circuit, etc. to generatenecessary signals by matrix calculation of current outputs from aplurality of photo acceptance units in the photodetector 5. Thenecessary signals include a high frequency signal (read data signal)corresponding to read data, a focus error signal FE and tracking errorsignal TE for use to make servo control, etc. Further, the necessarysignals include a groove wobbling signal, namely, a push-pull signal P/Pas a signal for detection of wobbles of a groove.

The read data signal output from the matrix circuit 9is supplied to abinarization circuit 11, focus error signal FE and tracking error signalTE are supplied to a servo circuit (servo processor) 14, and push-pullsignal P/P is supplied to a FSK demodulator 24.

The push-pull signal P/P as a groove wobbling signal from the matrixcircuit 9 is processed in a wobbling circuit system composed of the FSKdemodulator 24, and a wobble PLL 25 and address decoder 26.Specifically, an address is extracted from the push-pull signal P/P anda wobble clock WCK used to decode the ADIP information is supplied toother relevant circuit systems. The wobbling circuit system will bedescribed in detail later.

The read data signal from the matrix circuit 9 is binarized in thebinarization circuit 11and then supplied to an encoder/decoder 12 whichfunctions as a decoder during data reading and as an encoder during datawriting. When reading data, the encoder/decoder 12 makes demodulation ofrun-length limited code, error correction, de-interleaving, etc. toprovide read data.

For reading data, the encoder/decoder 12 generates, by PLL processing, aread clock synchronous with the read data signal, and decodes the dataon the basis of the read clock. At each time of data reading, theencoder/decoder 12 will cumulate the data decoded as above into a buffermemory 20. As a read output from the disc drive 30, data buffered in thebuffer memory 20 is read out and transferred.

An interface 13 also included in the disc drive 30 is connected to anexternal host computer 40 and transfers data to be recorded, read dataand various commands between the disc drive 30 and host computer 40.During data reading, read data decoded and stored in the buffer memory20will be transferred via the interface 13 to the host computer 40. Itshould be noted that a read command and write command and other commandsfrom the host computer 40 are supplied to a system controller 10 via theinterface 13.

On the other hand, data to be recorded from the host computer istransferred from the host computer 40 during data writing. The data tobe recorded is sent from the interface 13 to the buffer memory 20 whereit will be buffered. In this case, the encoder/decoder 12 encodes thebuffered data to be recorded by adding an error correction code,interleave and sub code, and encoding the data as data for write to theoptical disc 100.

There is also provided an encode clock generator 27 to generate anencode clock which will be a reference clock for data encoding when datarecording is made. The encoder/decoder 12 will use the encode clock formaking the above encoding operations. The encode clock generator 27generates the encode clock from the wobble clock WCK supplied from thewobble PLL 25. As mentioned above, the channel clock of the data to berecorded is of 66.033 kHz, for example, which is an integral multiple ofthe frequency fw1 of the monotone wobble. Since the wobble PLL 25generates a clock of the frequency fw1 of the monotone wobble, or aclock having a frequency which is an integral multiple of the frequencyfw1, as a wobble clock WCK, the encode clock generator 27 can easilygenerate an encode clock by dividing the frequency of the wobble clockWCK.

The data to be recorded generated through the encoding by theencoder/decoder 12 is adjusted in waveform in a write strategy 21 andthen sent as a laser drive pulse (write data WDATA) to the laser driver18. The write strategy 21 will make a recording compensation, that is,it will make a fine adjustment of optimum recording power for therecording layer characteristic, spot shape of the laser light, linearvelocity of recording, etc. and also adjust the waveform of the laserdrive pulse.

The laser driver 18 supplies the laser diode 4 with the laser drivepulse supplied as write data WDATA to drive the laser diode 4 foremission of laser light. Thus, a pit (phase-change pit) will be formedon the optical disc 100 correspondingly to the data to be recorded.

There is also provided an APC (auto power control) circuit 19 to controlthe laser driver 18 to keep a constant laser output power without beinginfluenced by the ambient temperature or other factors while monitoringthe laser output power on the basis of an output from the monitoringdetector 22. The APC circuit 19 is supplied with a target value of thelaser output from the system controller 10 to control the laser driver18 to attain the target value.

The servo circuit (servo processor) 14 generates various servo drivesignals from the focus error signal FE and tracking error signal TEsupplied from the matrix circuit 9 in order to implement servooperations. More specifically, the servo circuit 14 generates a focusdrive signal FD and tracking drive signal TD correspondingly to thefocus error signal FE and tracking error signal TE, and supplies them toa biaxial driver 16. This biaxial driver 16 will drive the focus coiland tracking coil in the biaxial mechanism 3 in the optical pickup 1.Thus, the optical pickup 1, matrix circuit 9, servo processor 14,biaxial driver 16 and biaxial mechanism 3 form together a tracking servoloop and focus servo loop. Also, the servo circuit 14 turns off thetracking servo loop in response to a track jump command from the systemcontroller 10 to provide a jump drive signal to the biaxial driver 16,thereby causing the optical pickup 1 to jump from one track to another.

The servo processor 14 generates a sled drive signal on the basis of asled error signal as a lowpass component of the tracking error signal TEand under the access control of the system controller 10, and suppliesthe signal to a sled driver 15. The sled driver 15 will drive the sledmechanism 8 correspondingly to the sled drive signal supplied from theservo processor 14. The sled mechanism 8 includes a mechanism (notshown) formed from a main shaft to support the optical pickup 1, sledmotor and transmission gear, etc. As the sled motor in the sledmechanism 8 is driven by the sled driver 15 correspondingly to the sleddrive signal, the optical pickup 1 is sledded accordingly.

There is also provided a spindle servo circuit 23 to control the spindlemotor 6 to rotate at a CLV. The spindle servo circuit 23 generates aspindle error signal SPE by acquiring the wobble clock WCK generated bythe wobble PLL 25, namely, information about a current rotation speedinformation of the spindle motor 6, and comparing it with informationabout a predetermined CLV reference speed.

Since during data reading, the read clock (reference clock for decoding)generated by the wobble PLL 25 in the encoder/decoder 21 is informationabout the current rotation speed of the spindle motor 6, the spindleerror signal SPE can also be generated by comparing the read clock withthe information about the predetermined CLV reference speed.

The spindle servo circuit 23 generates a spindle drive signalcorresponding to the spindle error signal SPE and supplies the signal toa spindle motor driver 17. According to the spindle drive signalsupplied from the spindle servo circuit 23, the spindle motor driver 17applies a three-phase drive signal, for example, to the spindle motor 6to cause the latter to rotate at a CLV. The spindle servo circuit 23also generates a spindle drive signal correspondingly to a spindlekick/brake control signal supplied from the system controller 10 tocause the spindle motor driver 17 to start, stop, accelerate ordecelerate the spindle motor 6.

Operations of the above-mentioned servo system and write/read system arecontrolled by the system controller 10 formed from a microcomputer. Thesystem controller 10 makes various control operations according tocommands supplied from the host computer 40. For example, in case thesystem controller 10 is supplied with a read command for transfer of adata recorded in the optical disc 100 from the host computer 40, it willfirst control the seek operation for access to a given address. Namely,the system controller 10 gives a command to the servo circuit (servoprocessor) 14 which will thus cause the optical pickup 1 to access atarget address specified by a seek command. Thereafter, the systemcontroller 10 controls necessary operations for transfer of data in aspecified data section to the host computer 40. Thus, data is read fromthe optical disc 100, decoded, buffered and otherwise processed and arequested data is transferred to the host computer 40.

Supplied with a write command from the host computer 40, the systemcontroller 10 will cause the optical pickup I to move to an addresswhere data is to be written. Then, the encoder/decoder 12 encodes thedata transferred from the host computer 40 as mentioned above. The writedata WDATA is supplied from the write strategy 21 to the laser driver 18as above, the data recording is effected.

The disc drive 30 shown as an example in FIG. 12 is connected to thehost computer 40. However, the disc drive according to the presentinvention is not connected to the host computer 40 as the case may be.In such a case, a control panel and display will be provided and thedata input/output interface will be different in construction from thatshown in FIG. 12. That is, the data recording and reproduction are to bemade according to corresponding operations of the control panel by theuser and there should be provided various data input/output terminals.

The disc drive according to the present invention may be constructed inmany other forms, and can be constructed as a disc drive dedicated fordata recording or reproduction.

Next, the wobbling circuit system included in the disc drive accordingto the present invention will be described.

Referring now to FIG. 13, the wobbling circuit is schematicallyillustrated in the form of a block diagram. FIG. 13 shows theconstruction of the FSK demodulator 24, wobble PLL 25 and addressdecoder 26 included in the wobbling circuit system. As shown, the FSKdemodulator 24 includes a bandpass filter 31, comparator 32, correlationdetection circuit 33, frequency detection circuit 34, discriminationcircuit 35, sync detection circuit 36 and a gate signal generationcircuit 37.

The push-pull signal P/P supplied as a wobbling signal from the matrixcircuit 9 is supplied to the bandpass filter 31 of the FSK demodulator24. The bandpass filter 31 has such a characteristic as passing twodifferent frequencies, that is, the two frequencies fw1 and fw2 used inthe aforementioned single-frequency part and FSK information bit part. Asignal component of the frequencies fw1 or fw2 passed through thebandpass filter 31 is binarized in the comparator 32. The binarizedpush-pull signal P/P is supplied to the wobble PLL 25, correlationdetection circuit 33 and frequency detection circuit 34. The wobble PLL25 is designed as a PLL to make phase comparison with respect to thebinarized push-pull signal P/P and generate a wobble clock WCKsynchronous with the push-pull signal P/P. However, a push-pull signalP/P for a period corresponding to the FSK information bit part of thewobble unit is masked by a gate signal GATE from the gate signalgeneration circuit 37 which will be described in detail later, whereby apush-pull signal P/P corresponding to the monotone wobble of thesingle-frequency part is locked. Thus, the wobble clock WCK has thesingle frequency fw1 itself or a frequency having a ratio of integralswith the single frequency fw1.

Note that the single-frequency part of the aforementioned wobble unithas a period sufficiently longer, for example, more than 10 timeslonger, than that of the FSK information bit part. Therefore, the PLLcan easily be pulled in.

The wobble PLL 25 makes phase comparison solely with the monotone wobbleof the frequency fw1 on the basis of the gate signal GATE. So, theresidual jitter of the wobble clock WCK generated as above isconsiderably reduced.

The wobble clock WCK thus generated is supplied to various circuits inthe FSK demodulator 24 and also to the address decoder 26, where it willbe used for FSK demodulation and decoding of the ADIP information. Also,as having been described with reference to FIG. 12, the wobble clock WCKis supplied to the end clock generator 27 and spindle servo circuit 23,where it will be used as above. In this case, since the wobble clock WCKis of a high accuracy with less residual jitter, the encode clock has animproved accuracy, the stability of recording operation is increased,and the stability of spindle servo control is also improved.

The correlation detection circuit 33 and frequency detection circuit 34are both to demodulate channel data embedded as an FSK information bitpart of the wobble unit. Therefore, at least one of these circuits 33and 34 may be provided in the FSK demodulator 24. However, when boththese correlation detection circuit 33 and frequency detection circuit34 are provided in the FSK demodulator 24, there takes place an effectwhich will be described later. The correlation detection circuit 33makes FSK demodulation by detecting a correlation over two periods ofthe wobble clock WCK, and demodulates the channel data. The frequencydetection circuit 34 makes FSK demodulation by counting edges in oneperiod of the wobble clock WCK, and demodulates the channel data. Theconstructions and operations of the correlation detection circuit 33 andfrequency detection circuit 34 will be described later. From each ofthese circuits' 33 and 34, there are extracted channel bit data aboutthe FSK-modulated wobble, that is, “0” and “1” as channel bits in unitsof a period of two monotone wobbles as shown in FIG. 4, and they aresupplied to the discrimination circuit 35.

The discrimination circuit 35 ANDs or ORs channel bit values suppliedfrom both the correlation detection circuit 33 and frequency detectioncircuit 34 and provides the ANDed or ORed channel bit value as aFSK-demodulated channel bit value. The discrimination circuit 35supplies the channel bit value thus calculated to the sync detectioncircuit 36. The sync detection circuit 36 detects a sync on the basis ofperiodicity of the supplied channel bit value.

As shown in FIG. 6, the cluster sync includes channel bit values “1”,“1” and “1”. Also, in the FSK information bit part of three channelbits, the top channel bit is always “1”, as shown in FIG. 6. On theother hand, in a period corresponding to the single-frequency part, theFSK-demodulated channel bit value is always “0”. Therefore, the first“1” after a series of the channel bit values “0” will be at the top ofthe FSK information bit pat, and the period including such “1” will beequivalent to a period of a wobble unit. By detecting such periodicity,it is possible to know the period of each wobble unit, and when a seriesof three channel bits “1”, “1” and “1” is detected in a wobble unit, itcan be determined that the wobble unit is the top one of 98 wobble unitsforming together a cluster sync, that is, one ADIP information.

The sync detection circuit 36 thus detects a sync timing and supplies async signal SY to the gate signal generation circuit 37 and addressdecoder 26. The gate signal generation circuit 37 generates a gatesignal GATE on the basis of the sync signal SY supplied from the syncdetection circuit 36. That is, since the period of a wobble unit isknown from the timing of the sync signal SY, the period of the FSKinformation bit part in the wobble unit can be known by counting clocksof the frequency fw1 on the basis of the sync signal SY. Thus, a gatesignal GATE to mask the period of the FSK information bit part isgenerated to control the phase comparing operation of the wobble PLL 25.

Note that although it has been described in the foregoing that thediscrimination circuit 35 ANDs or ORs the channel bit values from boththe correlation detection circuit 33 and frequency detection circuit 34,the discrimination circuit 34 will AND such channel bit values for aperiod down to the pull-in of the wobble PLL 25 to locking, made basedon the aforementioned sync detection and the gate signal GATE derivedfrom the detected sync.

As the channel bit values supplied from both the correlation detectioncircuit 33 and frequency detection circuit 34 are ANDed as above, thechannel bit values have improved reliability, whereby the sync can bedetected with an improved accuracy and less error. On the other hand,after the PLL is pulled in based on the sync detection, the operationshould be shifted from AND to OR since the sync can be guarded based onperiodicity. Especially, by ORing the channel bit values supplied fromboth the correlation detection circuit 33 and frequency detectioncircuit 34, missing of the detection due to a drop-out of the channelbit value can be reduced, whereby the ADIP information can be decodedwith improved reliability.

The discrimination circuit 35 acquires an FSK-demodulated channel bitvalue by ORing the channel bit values supplied from both the correlationdetection circuit 33 and frequency detection circuit 34 after the wobbleclock WCK becomes stable owing to the pull-in of the PLL, then makesdiscrimination between the data “0” and “1” as information bit of theFSK information bit part of each wobble unit represented by threechannel bits, and supplies the information bit to the address decoder26. The address decoder 26 can acquire address information of 98 bitshaving previously been explained with reference to Tables 2 and 3 byacquiring information bits with reference to the timing of the syncsignal SY, thus decodes an address value Dad embedded as a wobbledgroove, and supplies the address value to the system controller 10.

The correlation detection circuit 33 to make the FSK demodulation isconstructed as shown in FIG. 14.

The push-pull signal having been binarized by the comparator 32 shown inFIG. 13 is supplied to a delay circuit 112 and also to one of inputs ofexclusive OR (EX-OR) gate 113. The output of the delay circuit 112 isconnected to the other input of the EX-OR 113.

The wobble clock WCK is supplied to a IT measuring circuit 111. The ITmeasuring circuit 111 measures one period of the wobble clock WCK andcontrols the delay circuit 112 to provide a delay equal to one period ofthe wobble clock WCK. Therefore, the EX-OR 113 makes logical operationbetween the push-pull signal and the push-pull signal delayed by theperiod of IT. The output from the EX-OR 113 is subjected to extractionof lower frequency components in a lowpass filter 114 and binarized in acomparator 115. The binarized signal from the comparator 115 isdelivered as a latched output at a D-flip-flop 116 at the timing of thewobble clock WCK. The latched output provides an output “0” or “1” as achannel bit in units of a period of two monotone wobbles, and issupplied to the discrimination circuit 35.

The operating waveforms of the correlation detection circuit 33 areshown in FIGS. 15A to 15G. Note that the operating waveforms includepush-pull signals to be supplied for a period of the FSK information bitpart as the cluster sync. That is, the period shown as the FSKinformation bit pat in an input push-pull signal shown in FIG. 15B is abinarized series of nine wobbles of the frequency fw2, shown as thecluster sync in FIG. 6.

FIG. 15A shows the wobble clock WCK. The EX-OR 113 is supplied with abinarized push-pull signal shown in FIG. 15B and the binarized push-pullsignal, shown in FIG. 15C, which has been delayed by one wobble clockperiod in the delay circuit 112. Supplied with these push-pull signals,the EX-OR 113 provides an output as shown in FIG. 15D. This output isshaped by the lowpass filter 114 to have a waveform including only thelower frequency components as shown in FIG. 15E, and binarized in thecomparator 115 to have a waveform as shown in FIG. 15F. This signal issupplied to the D-flip-flop 116 from which it is delivered as latched atthe time of the wobble clock WCK. Thus, a signal shown in FIG. 15G willbe supplied as an FSK-demodulated channel bit value to thediscrimination circuit 35. The explanation is made here taking the FSKinformation bit part of the cluster sync as an example. So, the waveformfor the period corresponding to the FSK information bit pat is “H” for a6-wobble clock period as shown. That is, the channel bits will takevalues of “1”, “1” and “1” in units of the 2-wobble clock period (periodof two monotone wobbles). Namely, there will be provided a waveformshown as an address bit of the cluster sync in FIG. 4. If the waveformis an FSK information bit part indicating data “0” or “1”, the waveformfor this period will be as shown as address bits of data “0” or “1” inFIG. 4.

As having been described above, the optical disc according to thepresent invention uses the two different frequencies fw1 and fw2 forwobbling a track or groove. The frequency fw2 is 1.5 times higher thanthe frequency fw1, for example. The frequencies fw1 and fw2 are in sucha relation that each of them shows an even number of waves and an oddnumber of waves in a predetermined cycle. In such a case, the binarizedpush-pull signal and the binarized push-pull signal delayed by onewobble clock period of the frequency fw1 are in opposite phase to eachother for a wobble part of the frequency fw2, namely, for anFSK-modulated part corresponding to the channel bit value “1”, as willbe seen by comparison of FIGS. [5B and 15C. Thus, the FSK demodulationcan easily be done owing to the XC-OR logic for example. It should benoted that the demodulation can of course be done by the EX-OR logic aswell as any other logical operation.

The frequency detection circuit 34 also included in the FSK demodulator24 to make FSK demodulation is constructed as shown in FIG. 16.

The push-pull signal binarized in the comparator 32 shown in FIG. 13 issupplied to a rising edge count circuit 121 which counts a number ofrising edges of a push-pull signal in every cycle of the wobble clockWCK. Correspondingly to the result of counting, the rising edge countcircuit 121 provides an output “0” or “1”. The output of the rising edgecount circuit 121 is connected to one of inputs of an OR gate 123, andalso to a D-flip-flop 122. The signal supplied to the D-flip-flop 122 isdelayed one clock in the D-flip-flop 122 by the latch output at the timeof the wobble clock WCK, and supplied to the other input of the OR gate123. The OR output from the OR gate 123 is an output “0” or “1” as achannel bit in units of a period of two monotone wobbles, and suppliedto the discrimination circuit 35.

The operating waveforms of the frequency detection circuit 34 are shownin FIGS. 17A to 17E. The operating waveforms include push-pull signalsto be supplied for a period of the FSK information bit part as thecluster sync. That is, the period shown as the FSK information bit patin an input push-pull signal shown in FIG. 17B is a binarized series ofnine wobbles of the frequency fw2, shown as the cluster sync in FIG. 6.

FIG. 17A shows the wobble clock WCK. The rising edge count circuit 121counts a number of rising edges of a push-pull signal in every cycle ofthe wobble clock WCK. In FIG. 17B, each rising edge is shown with asmall circle, As seen from FIGS. 17B and 17C, the rising edge countcircuit 121 provides an output “1” when one rising edge has been countedwithin one wobble clock period while providing an output “1” when twosuch edges have been counted. The signal shown in FIG. 17C, thusprovided as the output, and a signal shown in FIG. 17D, delayed a periodIT by the D-flip-flop 122, are ORed by the OR gate 123 to provide anoutput as shown in FIG. 17E. The signal thus generated is supplied as anFSK-demodulated channel bit value to the discrimination circuit 35. Theexplanation is made here taking the FSK information bit part of thecluster sync as an example. So, the waveform for the periodcorresponding to the FSK information bit pat is “H” for a 6-wobble clockperiod as shown. That is, the channel bits will take values of “1”, “1”and “1” in units of the 2-wobble clock period (period of two monotonewobbles). Namely, there will be provided a waveform shown as an addressbit of the cluster sync in FIG. 4. If the waveform is an FSK informationbit part indicating data “0” or “1”, the waveform for this period willbe as shown as address bits of data “0” or “1” in FIG. 4.

Also, in the frequency detection circuit 34, the two differentfrequencies fw1 and fw2 are used for wobbling a track or groove. Thefrequencies fw1 and fw2 are in such a relation that each of them showsan even number of waves and an odd number of waves in a predeterminedcycle. Thus, the FSK demodulation can easily be done by the very simplecircuit construction as shown in FIG. 16.

Note that the above counting of rising edges may be replaced withcounting of falling edges.

Second Embodiment:

2-1 Wobbling Method

Next, the second embodiment of the present invention will be described.It should be noted that the second embodiment also concerns a disccalled “DVR” for example and the physical characteristics of the opticaldisc are similar to those having previously been described withreference to Table 1 and FIGS. 4A and 4B. The cutting apparatus for useto produce the optical disc and the disc drive for playing the opticaldisc are also basically similar to those having previously beendescribed concerning the first embodiment. So, the components of thesecond embodiment, also used in the first embodiment, will not bedescribed any more. Only the wobbling method and associated demodulatingmethod, different from those in the first embodiment, will be describedherebelow. In the explanation of the demodulating method, there willalso be described an example of the construction of a demodulationcircuit used in the disc drive included in the second embodiment andcorresponding to the FSK demodulator 24 shown in FIG. 12.

FIGS. 18A to 18F show the waveforms of wobbles which are when there areused an MSK (minimum key shifting) modulation also included in theaforementioned FSK modulation method for modulating an address of awobbled groove and a wobble detection window of L=4 for demodulation ofthe address. It should be noted that “L” indicates the length of thewobble detection window and “L=4” means that the detection unitcorresponds to a period of four monotone wobbles. When data waveform(channel bit) as address information to be recorded to a wobbled grooveis the waveform (data) in FIG. 1 8D, the data is pre-encoded to providepre-code data as shown in FIG. 18E. For example, the data is pre-encodedso that the pre-code data is set “1” at the time of logical inversion ofthe data. The MSK modulation is done using the pre-coded data to form astream as an MSK modulation signal as shown in FIG. 18F.

According to the second embodiment, two different frequencies fw1 andfw2 are used for the MSK modulation. The frequency fw1 is the same as acarrier frequency for the MSK modulation as shown in FIG. 18C. Thefrequency fw2 is 1.5 times higher than the frequency fw1 (it has awavelength equal to ⅔ of that of the frequency fw1), for example. Asshown in FIG. 18A for example, 1.5 wobbles of the frequency fw2 1.5times higher than the carrier frequency correspond to a pre-code data“1”, while one wobble of the frequency fw1 the same as the carrierfrequency corresponds to a pre-code data “0” as shown in FIG. 18B. Aperiod of 1.5 wobbles of the frequency fw2 corresponds to a period ofone wobble of the frequency fw1 (=carrier frequency).

FIGS. 19A to 19C show streams each of a wobble waveform including anMSK-modulated part. FIG. 19A shows a monotone bit which is a series ofwobbles of a single frequency (which is the frequency fw1). The monotonebit includes 56 monotone wobbles. FIG. 19B shows an ADIP bit has also aperiod of 56 monotone wobbles. The ADIP unit being of 12 of the 56monotone wobbles is an MSK information bit part. That is, the MSKinformation bit part is the pre-code data MSK-modulated with thefrequencies fw1 and fw2. The MSK information bit part includes addressinformation. The other 44 monotone wobbles in the ADIP bit are a seriesof 44 wobbles of the single frequency (=frequency fw1). FIG. 19C shows async bit having also a period of 56 monotone wobbles, of which 28monotone wobbles form together a sync unit. The pre-code data isMSK-modulated with the frequencies fw1 and fw2 as above. Syncinformation is represented by the pattern of the sync unit. The other 28monotone wobbles in the sync bit are a series of 28 wobbles of thesingle frequency fw1 (=carrier frequency). The ADIP bit, monotone bitand sync bit correspond to one bit which will form an address block (of83 bits) being one piece of address information (ADIP) and which will bedescribed below.

According to the second embodiment, one RUB (recording unit block) beinga unit of data recording includes three ADIP addresses, as shown inFIGS. 20A and 20B. As having previously been described with reference toFIGS. 7 and 8, “RUB” is a data unit consisting of one ECC block having arun-in and run-out added thereto. In this case, one RUB includes 498frames (498 rows). As shown in FIG. 20A, a section corresponding to oneRUB includes three ADIP address blocks. One address block is composed of83 bits as ADIP data. As shown in FIG. 19, since the ADIP bit andmonotone bit correspond to a period of 56 monotone wobbles, one addressblock corresponds to a period of 4648 (=83×56) monotone wobbles. Themonotone bit, sync bit and ADIP bit are as having previously beendescribed with reference to FIG. 19. The sync bit and ADIP bit areformed to have MSK-modulated waveform wobbles.

FIG. 20B shows the structure of one address block. The address block of83 bits includes a sync signal part of eight bits and a data part of 75bits. The sync signal part of eight bits includes four sync blocks eachof one monotone bit and one sync bit. The data part of 75 bits includes15 units each of one monotone bit and four ADIP bits. The monotone bit,sync bit and ADIP bit referred to herein have previously been describedwith reference to FIG. 19. The sync bit and ADIP bit provide a wobblehaving an MSK-modulated waveform.

First, the structure of the sync signal part will be described withreference to FIGS. 21A and 21B.

As shown in FIGS. 21A and 21B, the sync signal part is formed from foursync blocks “0”, “1”, “2” and “3”. Of the four sync blocks, the one “0”is formed from one monotone bit and sync “0”. The sync block “1” isformed from one monotone bit and sync “1”, the sync block “2” is formedfrom one monotone bit and sync “2”, and the sync block “3” is formedfrom one monotone bit and sync “3”.

In each sync block, the monotone bit is a waveform of 56 wobbles of thesingle frequency representing a carrier as previously mentioned, asshown in FIG. 22A.

The sync bits include the four types: sync bits “0” to “3” as above.Each of these four types of sync bits provides a wobble pattern as shownin FIGS. 22A, 22B, 22C and 22D. Each sync bit is composed of a sync unithaving a period of 28 monotone wobbles, and 28 monotone wobbles. Thesync units are different in pattern from each other. FIGS. 22B, 22C, 22Dand 22E show a wobble waveform pattern in a sync unit and a data patternas address information corresponding to the wobble pattern. As shown inFIGS. 18D and 18F, one channel bit as the channel informationcorresponds to a period of four monotone wobbles. A channel bit streamas the address information is pre-encoded into a pre-code data as shownin FIG. 18E to provide an MSK-modulated wobble waveform pattern.

First, the sync bit “0” forms a channel bit data stream “1010000” in thesync unit as shown in FIG. 22B. Namely, it provides wobblescorresponding to a pre-code data stream “1000100010001000000000000000”.More specifically, the sync bit “0” provides an MSK-modulated wobblepattern that a part of the pre-code data corresponding to “1” is 1.5wobbles of the frequency fw2 while a part corresponding to “0” is onewobble of the frequency fw1.

The sync bit “1” forms a channel bit data stream “1001000” in the syncunit as shown in FIG. 22C, and provides a wobble waveform correspondingto a pre-code data stream “1000 1000000010001 00000000000”.

The sync bit “2” forms a channel bit data stream “1000100” in the syncunit as shown in FIG. 22D, and provides a wobble waveform correspondingto a pre-code data stream “10001000000000001000 10000000”.

The sync bit “3” forms a channel bit data stream “1000010” in the syncunit as shown in FIG. 22E, and provides a wobble waveform correspondingto a pre-code data stream “10001000000000000000 10001000”.

The four patterns of the sync bits are laid in each sync block. Thus,when the disc drive can detect any of the four patterns of sync units inthe sync signal part, a synchronism can be attained between the syncunits.

Next, the structure of the data part of the address block will bedescribed with reference to FIGS. 23A and 23B.

As shown in FIGS. 23A and 23B, the data part is formed from 15 ADIPblocks “1” to “14”. Each of the ADIP blocks is of 5 bits. The five bitsof each ADIP block include one monotone bit and four ADIP bits.Similarly to the sync block, the monotone bit in each ADIP blockprovides a waveform of a series of 56 wobbles of the single frequencyrepresenting the carrier, as shown in FIG. 24A. Since one ADIP blockincludes four ADIP bits, fifteen ADIP blocks form together addressinformation of 60 ADIP bits. One ADIP block is composed of an ADIP unithaving a period of 12 monotone wobbles, and 44 monotone wobbles. FIG.24B show a wobble waveform pattern with the ADIP bit having a value “1”,and a data pattern as address information corresponding to the wobblewaveform. FIG. 24C shows a wobble waveform pattern with the ADIP bithaving a value “0”, and a data pattern as address informationcorresponding to the wobble waveform. Each of the ADIP bits “0” and “1”is represented by three channel bits in a period of 12 monotone wobbles.One channel bit is a period of four monotone wobbles. The ADIP bit “1”forms a channel bit data stream “100” in the ADIP unit as shown in FIG.24B. Namely, it provides a wobble waveform corresponding to a pre-codedata stream “1000000000”. More specifically, the ADIP bit “1” providessuch an MSK-modulated wobble pattern that a part of the pre-code datacorresponding to “1” is 1.5 wobbles of the frequency fw2 while a partcorresponding to “0” is one wobble of the frequency fw1. As shown inFIG. 24C. The ADIP bit “0” forms a channel bit data stream “010” in theADIP unit, namely, it provides a wobble waveform corresponding to apre-code data stream “000010001000”.

The above wobbling method according to the present invention ischaracterized as follows:

Wobbling is a sequence of ADIP bit and sync bit having waveforms,respectively, derived from MSK modulation of the information bit, and amonotone bit providing the single-frequency part based on the waveformof the single frequency fw1 (carrier frequency). Namely, theMSK-modulated parts in which the actual information bit is embedded willdiscretely be laid on a wobble track (groove). The discrete presence ofthe MSK-modulated parts contributes to a considerable reduction ofadverse affect of crosstalk even with a narrow track pitch. The MSKmodulation uses the two different frequencies fw1 and fw2. Of thesedifferent frequencies, the frequency fw1 is the same as the frequency ofthe monotone wobble (carrier frequency). The frequency fw2 is afrequency 1.5 times higher than the frequency fw1, for example, wherebythe relation between the frequencies fw1 and fw2 is such that thenumbers of both the frequencies are alternately even and odd in apredetermined cycle.

In the MSK information bit part, the period of four monotone wobbles isone channel bit (in case it corresponds to the length (L=4) of thewobble detection window) forming the information bit. The period lengthof the MSK-modulated part of the ADIP bit is a period of 12 monotonewobbles, that is, a period being an integral multiple of the cycle ofthe monotone wobble. These features will facilitate the FSKdemodulation. In the disc drive which will be described later, the MSKdemodulation can be easier because the demodulation is done in units ofa period of a plurality of wobbles, for example, a period of fourmonotone wobbles. The relation between the wobbling and data to berecorded is such that an integral number (three, for example) ofaddresses as ADIP information are used per RUB to provide matchingbetween the wobbled groove and data to be recorded. In the MSKinformation bit part, the phases are continuous at the point of shiftingbetween the frequencies fw1 and fw2. Thus, the wobbling by the MSKmodulation will not include any high frequency component as in thewobbling by the PSK modulation.

2-2 Demodulation

The demodulation corresponding to the wobbling method in the secondembodiment of the present invention will be described herebelow. Itshould be noted that the disc drive is similar in construction to thatshown in FIG. 12 and circuit components provided instead of the bandpassfilter 31, comparator 32, correlation detection circuit 33 and frequencydetection circuit 34 in the FSK demodulator 24 in FIG. 13 will bedescribed with reference to FIG. 25.

For the MSK demodulation, there are provided bandpass filters 151 and152, multiplier 153, adder 154, accumulator 155, sample and hold circuit156 and a slicer 157 as shown in FIG. 25. It should be noted that thecomponents such as wobble PLL 25, address decoder 26 and encode clockgenerator 27, etc. included in the second embodiment are similar tothose shown in FIG. 12 and so will not be described any more. The outputfrom the circuit shown in FIG. 25 (output from the slicer 157) issupplied to the discrimination circuit 35 included in the FSKdemodulator 24 shown in FIG. 13. Namely, it is assumed that thediscrimination circuit 35, sync detection circuit 36 and gate signalgeneration circuit 37 shown in FIG. 13 are similarly provided downstreamof the circuit shown in FIG. 25.

A push-pull signal P/P supplied as a wobbling signal from the matrixcircuit 9 in FIG. 12 is supplied to each of the bandpass filters 151 and152 in FIG. 25. The bandpass filter 151 has such a characteristic as toallow frequency bands corresponding to the frequencies fw1 and fw2 topass through it. The bandpass filter 151 extracts a wobble component,that is, MSK-modulated wave. On the other hand, the bandpass filter 152has such a narrow-band characteristic as to pass only the frequency fw1,that is, a carrier component, and thus it extracts the carriercomponent. The adder 153 multiplies outputs from the bandpass filters151 and 152. The product from the addern 153 and an output from theaccumulator 155 are supplied to the adder 154. The accumulator 155 iscleared by a clear signal CLR in units of a period of four wobbles (incase L=4) or a period of two wobbles (in case L=2). Therefore, theaccumulator 155 will provide an integrated value for the period of fouror two wobbles.

The output from the accumulator 155 is held in the sample and holdcircuit 156. The sample and hole circuit 156 samples and holds thesignal at the timing of a hold control signal sHOLD. The output from thesample and hold circuit 156 is binarized by the slicer 157 formed as acomparator. The binarized data output is a channel bit data formingaddress information, and supplied to a downstream circuit, namely, tothe discrimination circuit 35 as shown in FIG. 13. In the discriminationcircuit 35, the data is discriminated to have a value as an ADIP bit orsync bit. The ADIP bit thus discriminated is supplied to the addressdecoder 26 shown in FIGS. 12 and 13 where it will have the ADIP addressthereof decoded. The sync bit will be processed in the sync detectioncircuit 32 in FIG. 12 in the same manner as described with reference toFIG. 12.

The MSK demodulation will be described with reference to waveforms shownin FIGS. 26A and 26B. The waveforms are ones developed when the length Lof the wobble detection window is L=4.

FIG. 26A shows pre-code data, a wobble waveform MSK (L=4) formedcorrespondingly to the pre-code data, and a carrier frequency as anoutput from the bandpass filter 152 (BPF out). FIG. 26B shows an outputfrom the adder 153 (Demod out), output from the accumulator 155 (Int(L=4)) and an output from the sample and hold circuit 156 (h (L=4)).Multiplication in the multiplier 153 of the wobble waveform MSK (L=4) asshown in FIG. 26A by the carrier frequency (BPF out) provides the signal(Demod out) as shown in FIG. 26B. The accumulator 155 and adder 154provide the signal (Int (L=4)) integrated in units of four wobbles. Theintegrated signal (Int (L=4)) is sampled and held in the sample and holdcircuit 156 in units of four wobbles as well to provide the output (h(L=4)). The waveform of the output (h (L=4)) is binary-sliced by theslicer 157 to detect a channel bit data yet to pre-code.

FIGS. 27A and 27B show waveforms developed when the length L of thewobble detection window is L=2. As in FIGS. 26A and 26B, pre-code data,wobble waveform MSK (L=2), carrier frequency (BPF out), output from theadder 153 (Demod out), output from the accumulator 155 (Int (L-2)) andan output from the sample and hold circuit 156 (h (L=2)) are shown inFIGS. 27A and 27B. Multiplication in the multiplier 153 of the wobblewaveform MSK (L=2) by the carrier frequency (BPF out) provides thesignal (Demod out) as shown in FIG. 26B. The accumulator 155 and adder154 provide the signal (Int (L=2)) integrated in units of two wobbles.The integrated signal (Int (L=2)) is sampled and held in the sample andhold circuit 156 in units of two wobbles to provide the output (h(L=2)). The waveform of the output (h (L=2)) is binary-sliced by theslicer 157 to detect a channel bit data yet to pre-code.

According to the present invention, the length of the wobble detectionwindow can be increased to a period of a plurality of wobbles, wherebythe MSK demodulation can be done easily and accurately.

As will be seen through comparison between the integrated signal (Int)and sampled and held signal (h) shown in FIGS. 26A and 26B and FIGS. 27Aand 27B, respectively, the length (L=4) of the wobble detection windowwill provide an integrated area 2 times larger than that provided by thelength (L=2), and thus the signal will be 2 times larger. The noise whenL=4 will not be 2 times larger than that when L=2 but √{square root over( )}2 times larger.

Thus, when L=4 in total, the signal-to-noise (S/N) ratio will be betterby 3 dB than with L=2. Therefore, the bit error with L=4 is smaller thanthat with L=2. Therefore, since the length of the wobble detectionwindow is increased owing to the wobbling method according to thepresent invention, it will be understood that the MSK demodulation andADIP decoding are more reliable.

In the foregoing, the present invention has been described concerningthe embodiments of the disc, cutting apparatus for use to produce thedisc and the disc drive in which the disc is used as a recording medium.However, the present invention is not limited to such embodiments butmay be modified in various forms without departing from the scope of thepresent invention, defined by the claims given later.

INDUSTRIAL APPLICABILITY

As having been described in the foregoing, the disc-shaped recordingmedium according to the present invention has formed thereon wobbleseach of which is a series of predetermined signal units each consistingof an FSK information bit part and a single-frequency part correspondingto the waveform of a single frequency. Since FSK-modulated (orMSK-modulated) parts are thus discretely formed, the influence of acrosstalk from adjacent wobbled tracks is reduced, which is verysuitable for an improvement of the recording density with a smallertrack pitch. That is, the present invention is suitably usable as thewobbling method for a large-capacity disc.

The cutting apparatus according to the present invention includes meansfor generating a series of predetermined signal units each composed of asignal part resulted from FSK modulation of information bit and a signalpart of a single frequency. Namely, the one-beam cutting method can beadopted in the cutting apparatus for use to produce a disc-shapedrecording medium intended for a larger recoding capacity.

The disc drive according to the present invention is a high-performanceapparatus in which information such as an address can be extracted fromthe wobbled groove formed on the disc-shaped recording medium. Moreparticularly, the clock reproduction unit can easily and accuratelygenerate, by the PLL, a wobble reproduction clock on the basis of asignal corresponding to a single frequency part of a wobbling signal,having a waveform of the single frequency. The disc drive can operatestably by generating an encode clock for processing the data to berecorded, and making spindle servo control based on the wobblereproduction clock. The PLL can operate based on a gate signal generatedon the basis of the sync detection to provide a stable PLL operationonly with a signal corresponding to the single-frequency part of thewobbling signal. Thus, the PLL permits a quicker pull-in to locking anda more accurate clock reproduction.

Further, the wobble formed on the disc-shaped recording medium accordingto the present invention includes a single-frequency part of which thelength is sufficiently longer than that of the FSK information bit part.So, easy pull-in to locking of the PLL using the single-frequency partis possible. The FSK demodulation of a signal corresponding to the FSKinformation bit part of the wobble can be attained easily and accuratelyowing to the correlation detection or frequency detection.

1. A disc-shaped recording medium comprising: a spiral, wobbled track asa groove or land along which data is recorded, wherein at least aportion of the wobble of the track includes a series of predeterminedsignal units including one or more FSK information bit partscorresponding to a waveform resulted from FSK (frequency shift keying)modulation of information bit and one or more single-frequency partscorresponding to the waveform of a single frequency, wherein the FSKmodulation is an MSK (minimum shift keying) modulation.
 2. Thedisc-shaped recording medium as set forth in claim 1, wherein twodifferent frequencies are used in the FSK modulation; one of thefrequencies being the same as the single frequency while the other isdifferent from the single frequency; and these frequencies being in sucha relation that each of the frequencies has an even number of wobblesand an odd number of wobbles alternately in a predetermined cycle. 3.The disc-shaped recording medium as set forth in claim 2, wherein theother frequency has a frequency 1.5 times or 1/1.5 times higher thanthat of the one frequency.
 4. The disc-shaped recording medium as setforth in claim 1, wherein in the FSK information bit part, a 2-wobbleperiod of a frequency as the single frequency corresponds to one channelbit as information bit.
 5. The disc-shaped recording medium as set forthin claim 1, wherein the period length of the FSK information bit part isan integral multiple of the period of the single frequency.
 6. Thedisc-shaped recording medium as set forth in claim 1, wherein in thepredetermined unit, the period length of the single-frequency part ismore than 10 times of that of the FSK information bit part.
 7. Thedisc-shaped recording medium as set forth in claim 1, wherein anintegral multiple in the predetermined unit corresponds to a time lengthof a recording unit of data to be recorded to the track.
 8. Thedisc-shaped recording medium as set forth in claim 1, wherein thechannel clock frequency of data to be recorded to the track is anintegral multiple of the single frequency.
 9. The disc-shaped recordingmedium as set forth in claim 1, wherein a frequency as the singlefrequency is a one between a tracking servo frequency band and a readsignal frequency band.
 10. The disc-shaped recording medium as set forthin claim 1, wherein the FSK information bit part is formed on the basisof a waveform resulted from FSK modulation of information bit as addressinformation.
 11. The disc-shaped recording medium as set forth in claim1, wherein the FSK modulation for the FSK information bit part uses twodifferent frequencies of which the one is continuous in phase with theother at the point of shift from one to the other.
 12. (canceled) 13.The disc-shaped recording medium as set forth in claim 1, wherein in theFSK information bit part resulted from MSK modulation of the informationbit, a predetermined wobble period of the frequency as the singlefrequency corresponds to one channel bit as information bit.
 14. Thedisc-shaped recording medium as set forth in claim 13, wherein: the FSKinformation bit part resulted from MSK modulation of the information bitincludes two different frequencies of which the one is the same as thesingle frequency and the other is a frequency x times higher than thesingle frequency; and the predetermined wobble period includes a periodof four wobbles of the one frequency and a period of x wobbles of theother frequency and three wobbles of the one frequency.
 15. Thedisc-shaped recording medium as set forth in claim 14, wherein x=1.5.16. A cutting apparatus comprising: means for generating a series ofpredetermined signal units including a signal part resulted from FSKmodulation of information bit and one or more signal parts of a singlefrequency, when the FSK modulation is an MSK (minimum shift keying)modulation; means for generating a drive signal on the basis of thesignal supplied from the signal generating means; a laser source means;means for deflecting laser light from the laser source means on thebasis of the drive signal from the drive signal generating means; andmeans for cutting a disc substrate by radiating the laser light to thedisc substrate through the laser light deflecting means to form, on thedisc substrate, a wobbled track including the series of predeterminedunits each composed of the FSK information bit part based on a waveformresulted from FSK modulation of the information bit and the one or moresingle-frequency parts based on the waveform of the single frequency.17. A disc drive for recording or reproducing data to or from adisc-shaped recording medium having a spiral, wobbled track as a grooveor land along which data is to be recorded and in which at least aportion of the wobble of the track includes a series of predeterminedsignal units including one or more FSK information bit partscorresponding to a waveform resulted from FSK modulation of informationbit and one or more single-frequency parts corresponding to the waveformof a single frequency, when the FSK modulation is an MSK (minimum shiftkeying) modulation, the apparatus comprising: a head means for radiatinglaser light to a track to generate a return light signal; means forextracting a wobbling signal about wobbling of the track from the returnlight signal; and a wobbling information decoding means for making FSKdemodulation of the wobbling signal to decode information represented bythe information bit.
 18. The disc drive as set forth in claim 17,wherein the wobbling information decoding means includes a clockreproduction unit to generate, by a PLL, a wobble reproduction clock onthe basis of a signal corresponding to a single-frequency part of thewobbling signal, an FSK demodulator to make FSK demodulation of thewobbling signal corresponding to the FSK information bit part of thewobbling signal to provide demodulation data, and a decoder to decoderequired information composed of the information bit from thedemodulation data supplied from the FSK demodulator.
 19. The disc driveas set forth in claim 18, wherein the FSK demodulator includes acorrelation detection circuit to make FSK demodulation by detecting acorrelation as to the wobbling signal.
 20. The disc drive as set forthin claim 19, wherein the correlation detection circuit detects acorrelation between the wobbling signal and a delay signal resulted fromdelaying of the wobbling signal by a period of the wobble reproductionclock.
 21. The disc drive as set forth in claim 18, wherein the FSKdemodulator includes a frequency detection circuit to make FSKdemodulation by detecting a frequency of the wobbling signal.
 22. Thedisc drive as set forth in claim 21, wherein the frequency detectioncircuit detects a number of rising edges or falling edges of thewobbling signal, existent within one period of the wobble reproductionclock.
 23. The disc drive as set forth in claim 18, wherein: the FSKdemodulator includes a correlation detection circuit to make FSKdemodulation by detecting a correlation as to the wobbling signal and afrequency detection circuit to make FSK demodulation by detecting afrequency of the wobbling signal; and the decoder decodes the requiredinformation using both the demodulation data demodulated by thecorrelation detection circuit and that demodulated by the frequencydetection circuit.
 24. The disc drive as set forth in claim 23, whereinthe decoder decodes the required information from a logical product ofthe demodulated data from the correlation detection circuit and thatfrom the frequency detection circuit when the PLL is being pulled in theclock reproduction unit, and it decodes the required information from alogical sum of the demodulated data from the correlation detectioncircuit and that from the frequency detection circuit when the PLL isstable in the clock reproduction unit.
 25. The disc drive as set forthin claim 18, wherein: the decoder includes a gate generator to generatea gate signal for the PLL in the clock reproduction unit based on thefact that it decodes sync information as one of the requiredinformation; and the PLL functions on the basis of the gate signal toprovide a PLL operation based solely on a part, corresponding to thesingle frequency, of the wobbling signal.
 26. The disc drive as setforth in claim 18, further comprising a spindle servo means for makingspindle servo control using the wobble reproduction clock.
 27. The discdrive as set forth in claim 18, further comprising means for generatingan encode clock synchronous with the wobble reproduction clock and whichis to be used for encoding data to be recorded.
 28. The disc drive asset forth in claim 18, wherein the wobbling information decoding meansincludes an MSK demodulator for making MSK modulation of an MSKmodulation signal corresponding to the FSK information bit part of thewobbling signal to generate demodulation data.
 29. The disc drive as setforth in claim 28, wherein the MSK demodulator demodulates the MSKmodulation signal in units of a predetermined wobble period of thefrequency as the single frequency to provide the modulation signal.